Connect with TRB

LIMITATIONS TO THE USE OF THIN SURFACINGS AND UNBOUND AGGREGATE BASES FOR PAVEMENTS

PAVEMENT DESIGN PROCEDURES WHICH ESTIMATE THE THICKNESS OF COVER NECESSARY OVER THE SUBGRADE AND SUB-BASE, OR AN OVERALL THICKNESS INDEX (STRUCTURAL NUMBER), REQUIRE SUPPLEMENTATION BY SPECIFICATIONS FOR FACTORS SUCH AS THE SURFACINGS THICKNESS AND BASECOURSE QUALITY IN ORDER TO ENSURE A BALANCED DESIGN. MOST CURRENT SOUTH AFRICAN DESIGN INCLUDE SPRAY AND CHIP OR THIN PREMIX SURFACINGS OVER UNBOUND AGGREGATE BASES, ALTHOUGH INCREASING USE IS NOW BEING MADE OF BOUND BASES. EXCEPT FOR A FEW SHORT HEAVILY TRAFFICKED ROUTES, SOUTH AFRICAN ROADS CARRY RELATIVELY LIGHT TRAFFIC AT PRESENT, BUT MAJOR INCREASES ARE EXPECTED TO OCCUR AND THE NEW FREEWAYS ARE LIKELY TO ATTRACT HEAVY TRAFFIC. REVIEWS OF OVERSEAS FULL-SCALE ROAD EXPERIMENTS AND DESIGN SPECIFICATIONS REVEAL THAT CONSIDERABLY GREATER THICKNESSES OF SURFACING, AND FREQUENTLY ALSO THE USE OF BITUMEN OR CEMENT BOUND BASES ARE REQUIRED ON HEAVILY TRAFFICKED ROADS. CONDITIONS IN CALIFORNIA AND TEXAS ARE THOSE MOST CLOSELY RELATED TO THOSE PERTAINING IN SOUTH AFRICA, AND THE SPECIFICATIONS USED IN THESE STATES SHOULD, AT LEAST, BE TAKEN INTO CONSIDERATION IN PREPARING DESIGNS FOR HEAVILY TRAFFICKED ROADS. /RRL(A)/